As critical dimensions of semiconductor devices shrink and semiconductor technology nodes (about half of a pitch) decrease, the 193 nm immersion lithography for forming a patterned mask layer encounters its physical limitations. Pitches between adjacent patterns are too small. The adjacent patterns may be undesirably connected with each other due to optical proximity effect (OPE). Conventional solutions include use of a double patterning method.
In the double patterning method, a pattern to be formed may be first split into two patterns including a first pattern and a second pattern. The critical dimensions of the first pattern and the second pattern can be twice of that of the pattern to be formed. By using such double patterning method, the optical proximity effect (OPE) generated, due to the overly small pitches between adjacent patterns, can be reduced.
FIGS. 1-2 illustrate a local interconnect structure formed by a conventional method. As shown in FIGS. 1-2, a first dielectric layer 101 is formed on a substrate that has semiconductor elements formed thereon. A plug contact 102 is formed in the first dielectric layer 101, and on the source, the drain and the gate 105. Then, an aluminum layer is formed on surface of the first dielectric layer 101. A double patterning method is used to etch the aluminum layer to form an L-shaped local interconnect structure 104. The L-shaped local interconnect structure 104 is connected to the plug contact 102 on the source or the drain at one end and is electrically connected to the plug contact on the gate electrode 105 at the other end.
When using the double patterning method to form the L-shaped interconnect structure 104, an L-shaped pattern can be divided into two line-shaped segments perpendicularly configured and intersected at one end of each line-shaped segment. The two line-shaped segments are used as an etch mask to etch the aluminum layer to form the L-shaped local interconnect structure 104.
However, as critical dimensions of semiconductor devices shrink, optical proximity effect (OPE) and undesirable connections between adjacent patterns may occur during the double patterning. The L-shaped local interconnect structure 104 may thus have large deformation, and the subsequently-formed local interconnect structures thus have un-accurate pattern. For example, subsequently a local interconnect structure may be formed on a spot where the local interconnect structure is not designed to be formed, which may cause leakage current to the semiconductor device. More seriously, if the formed L-shaped local interconnect structure is broken, the semiconductor device will not work.